A fiber optic focusing device may be used to focus a parallel light beam onto the end of a glass fiber. In prior art focusing devices, a focusing lens is typically held in a threaded focusing ring which is itself threaded into a holder. Focus adjustments are made by rotating the ring within the holder to move the lens along the optical axis. In such prior art devices, the use of threads often causes tilting of the lens during rotation. In addition, it is often very difficult to lock the lens in a desired position with sufficient accuracy.
In accordance with the illustrated preferred embodiment of the present invention, a fiber optic focusing device is smoothly adjustable without lens tilting. The device includes a lens system that is linearly displaceable along the optical axis to permit focus adjustments. The lens system is held by a holder which is itself contained within a frame. Setscrews in the frame roughly perpendicular to the optical axis engage the holder to displace it along the optical axis as desired. For enhanced accuracy, the setscrews may include microthreads and may be guided in corresponding threaded bores. In addition, the frame may include a clamping screw for locking the holder in position relative to the frame. Since the lens system is fixed rigidly in the holder and the holder is seated in a precise parallel guide without tilting, the focusing device may be adjusted with a high degree of precision.